Spinning of polymer mixtures is known from a number of publications:
EP 0 035 796 A (Teijin) describes synthetic fibers, inter alia of polyester or polyamide, which comprise 1-15 wt. % of a polysulphone polymer having a high glass transition point of T.sub.G .gtoreq.150.degree. C. The additive remains in the matrix in a spheroidal form and influences the surface structure of the filaments and the thread friction. The spinning speed is 2000-5500 m/min.
EP 0 041 327 B (ICI) discloses fibers of PET or PA-6.6 which comprise 0.1-10 wt. % of a further polymer having anisotropic properties (LCP types). The spinning speeds are 1000 to 5000 m/min. A speed suppression (WUSS) is achieved by a higher elongation at break of the strand and therefore higher stretching ratios and an increase in productivity.
EP 0 080 274 B (ICI) relates to fibers of PET, PA-6.6 or PP which comprise 0.1-10 wt. % of a further polymer which is present in the melt with an average particle size of 0.5-3 .mu.m and is deformed to fibrils during melt spinning. The spinning speeds are 2000 to 6000 m/min, a speed suppression (WUSS: wind up speed suppression) of at least 20% being achieved by a higher elongation at break or lower birefringence of the (PET) strand, and therefore higher stretching ratios and an increase in productivity. Preferred additive polymers are polyethylene glycol or PA-6.6 for PET or polyolefins for PA-6.6. The effect reacts markedly to production parameters, such as throughput, spinning temperature, type of mixing or type of extruder. A transfer to production plants of different capacity, types of equipment or titer programs is made difficult by this sensitivity. We attribute the negative behavior to an unsuitable additive with too low a viscosity, too low a glass transition point and the tendency to crystallize.
JP 56-91013 A (Teijin) discloses a non-stretched polyester yarn, in which, by addition of 0,5-10 wt.-% of a styrene polymer, an improved productivity is achieved by increasing the elongation at break of the strand at speeds of between 850-8000 m/min, preferably .gtoreq.2500 m/min, with correspondingly higher stretching ratios. No requirements are disclosed for the polymer mixture and the non-stretched yarn for the stretch texturizing.
EP 0 047 464 B (Teijin) relates to a non-stretched polyester yarn, in which, by addition of 0,2-10 wt.-% of a polymer of the type .paren open-st.CH.sub.2 --CR.sub.1 R.sub.2 .paren close-st..sub.n, such as poly(4-methyl-1-pentene) or polymethyl methacrylate, an improved productivity is obtained by increasing the elongation at break of the strand at speeds of between 2500-8000 m/min, with correspondingly higher stretching ratios. A fine and uniform dispersion of the additive polymer by mixing is needed, it being necessary for the particle diameter to be .ltoreq.1 .mu.m to avoid the formation of fibrils. The combined effect of three properties is said to be decisive for the action--the chemical structure of the additive, which scarcely allows extension of the additive molecules, the low mobility and the compatibility between the polyester and additive. The measures serve to increase productivity. No requirements are disclosed for the stretch texturizing.
EP 0 631 638 B (AKZO) describes fibers of predominantly PET which contains 0.1-5 wt. % of a polymethacrylic acid alkyl ester imidized to the extent of 50-90%. The fibers obtained at speeds of 500-10,000 m/min and subsequently finally stretched have a higher initial modulus. Spinning at very high speeds (such as 8000 m/min) is said to be possible with conventional thread breakage counts. Up to 8000 m/min partly oriented yarns which are not yet stretched to the final elongation and can be processed e. g. to texturized yarns are obtained. In the examples of industrial yarns, the influence on the modulus cannot be readily reconstructed; in general, the strengths achieved are lower, which is a considerable disadvantage for this product. For textile applications, only stretched yarns are described. The associated unstretched yarns at a spinning speed of from 6000 m/min show elongations at break of .ltoreq.65.3%, which are probably not processable by stretch texturizing because of the accompanying high crystallization (shrinkage at the boil .ltoreq.6.5%).
Spinning of polymer mixtures to synthetic fibers has the aim of obtaining a higher elongation at break in the strand at a particular spinning speed than without modification by an additive polymer. As a result, a higher stretching ratio for production of the final yarn is said to be possible, which is said to have the effect of a higher productivity of the spinning unit. According to EP 0 041 327 B, for example, a production gain of: ##EQU2## where E/E' are the non-modified/modified elongations at break, is to be expected. Investigation of the formula shows that the effect is the greatest at high increases in elongation (E'-E). However, elongations which are too high and therefore a reduced degree of orientation of the strand are unsuitable for processing in high-speed stretch texturizing processes.
Another way of increasing productivity is described in EP 0 080 274 B by the parameter WUSS.gtoreq.20%. At a spinning speed which is at least 20% higher, the same elongation at break in the strand is obtained as at the correspondingly lower speed with non-modified polymer. No running properties in the spinning mill at a higher speed and during further processing or properties of the final yarns produced there are disclosed. It has been found that the average particle sizes claimed, of .gtoreq.0.5 .mu.m, are unsuitable for commercial processing of the mixture, since such particle distributions lead to many capillary and thread breakages.
Increasing production is targeted at improving the profitability of the production process. This is curtailed again to a certain extent by production difficulties and expensive high-speed equipment. The additional costs for the additive polymer have a substantial influence, so that, depending on the amount added, there is even a zero point for the profitability. The availability of the additive polymers on the market also plays an important role. For these reasons, a large number of the additives described in the literature are eliminated from large-scale industrial conversion.
The producer or processor must take into account the entire production chain, and cannot stop at increasing production of a component step (e. g. spinning). The secondary processes should not be impaired. In particular, one of the main aims of this invention is not to curtail and preferably to improve the further processing conditions in the secondary steps, in spite of an increased spinning speed.
Very high elongations at break are thus mentioned in the prior art for polymer mixtures also for high spinning speeds, these characterizing a marked reduction in the degree of orientation. As is known, such strands are not storage-stable, and cannot be spread and processed at high speeds in friction texturizing processes. Elongations at break of &lt;70% stated for high spinning speeds in turn indicate a considerable degree of crystallization, which reduces the strengths which can be achieved in the texturizing process.